Amide-imide polymers are a relatively new class of organic compounds known for their solubility in nitrogen-containing organic solvents when in the largely polyamide form. The major application of the amide-imide polymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,661,832 (1972); 3,494,890 (1970); and 3,347,828 (1967).
Compositions prepared from isophthalic acid and diamines and aliphatic diamines have found application in coatings and films. The prior art on this is summarized in U.S. Pat. No. 3,444,183 (1969).
Reinforced polyhexamethylene isophthalamides have been used to produce articles as disclosed in U.S. Pat. No. 4,118,364 (1978). However, the physical properties of these reinforced polyhexamethylene isophthalamides are insufficient for use in engineering plastics since their tensile strength and continuous service temperature do not meet those required for engineering plastics.
U.S. Pat. Nos. 3,817,921 (1974) and 3,897,497 (1975) disclose polyamide-imides which are both tractable and soluble in polar solvents as well as stable at high temperatures prepared by the condensation polymerization of aromatic diamines or oligomers containing oxygen, sulfone, and optionally alkylidene linkages with trimellitic acid, trimellitic acid anhydride, or trimellitic anhydride acid chloride.
U.S. Pat. No. 4,313,868 (1982) discloses copolymers and molding compositions prepared from acylhalide derivatives of dicarboxylic acids, acylhalides of tricarboxylic aromatic anhydrides and aromatic diamines. That reference also discloses glass-filled copolymers. These products, useful as engineering plastics, have a tendency to have flow problems. These problems are overcome when about 1 to about 10 percent phthalic anhydride, aniline or trimellitic anhydride or a mixture of these is added to the polymer.
U.S. Pat. No. 4,136,085 (1979) discloses that the addition of phthalic anhydride to compositions based on the acylhalide derivative of trimellitic anhydride and diamines did not improve the flow properties of the polymer. Applicants have discovered that when phthalic anhydride, aniline, trimellitic anhydride or a mixture of these is added to the polymer of this invention, the flow is greatly improved.
The general object of this invention is to provide amide-imide and polyamide copolymers comprising about 1 to about 10 percent phthalic anhydride moieties, aniline moieties, trimellitic anhydride moieties or a mixture of two or more of these moieties. A more specific object of this invention is to provide polyamide-imide polymers prepared from aromatic diamines such as 2,2-bis(4-p-aminophenoxy)phenyl)propane, bis(4-(p-aminophenoxy)phenyl)sulfone, m-phenylene diamine, oxybis(aniline), m-toluene diamine, neopentene diamine and 2,2,2, trimethylhexamethylene diamine or a mixture containing any two or more of thee diamines, and mixtures of an acylhalide derivative of an aromatic tricarboxylic anhydride and about 1 to about 10 percent phthalic anhydride, aniline, trimellitic anhydride or a mixture of these wherein the physical properties of said polymers are optimal as molded and do not require an annealing step to enhance physical properties and said polymer can be remolded if annealed. A more specific object of this invention is to provide a polyamide-imide polymer with improved melt flow properties said polymer produced from bis(4-(p-aminophenoxy)phenyl)sulfone, 4-trimellitoyl anhydride chloride, about 1 to about 10 percent aniline as a capping agent and about 1 to about 5 weight percent of an amorphous polyamide. Another object of this invention is to provide a process for incorporating 1 to about 10 percent phthalic anhydride, aniline, trimellitic anhydride, or a mixture of these into polyamide-imide polymers. Other objects appear hereinafter.
The use of polyamide-imide polymers as engineering plastics has been limited by the relatively high cost of the polyamide-imides and to a lesser extent by the post molding annealing process to enhance the physical properties of the molded polyamide-imide parts. Thus, when the inherent cost of polyamides-imides is decreased and/or when a polyamide-imide is discovered that does not require a post molding heat treating or solid stating step, hereinafter referred to as annealing, to obtain optimal physical properties, the commercial application of these polymers will be greatly expanded. The polyamide-imide polymers of this invention have significant cost advantages over prior art compositions and in addition the as-molded physical properties of parts produced from the polyamide-imide of this invention are optimal as-molded and do not require an annealing step to enhance the physical properties.
The improved polyamide-imide polymers of this invention are prepared by reacting a mixture of an acyl halide derivative of an aromatic tricarboxylic acid anhydride with one aromatic diamine, a mixture of aromatic diamines, or a mixture of aromatic aliphatic diamines. The resulting polymers are polyamides wherein the linking groups are predominantly amide groups, although some may be imide groups, and wherein the structure contains free carboxylic acid groups which are capable of further reaction. Such polyamides are moderate molecular weight polymeric compounds having, in their molecule, units of: ##STR1## and units of: ##STR2## and, optionally, units of: ##STR3## wherein the free carboxyl groups are ortho to one amide group, Z is an aromatic moiety containing 1 to 4 benzene rings or lower-alkyl-substituted benzene rings and wherein R.sub.1, R.sub.2 and R.sub.3 are the same for homopolymers and are different for copolymers and are divalent aromatic or aliphatic hydrocarbon radicals. These hydrocarbon radicals may be a divalent aromatic or aliphatic hydrocarbon radical of from 6 to about 10 carbon atoms, or two divalent aromatic hydrocarbon radicals each of from 6 to about 10 carbon atoms joined directly or by stable linkages such as --O--, methylene, --CO--, --SO.sub.2 --, --S--; for example, --R'--O--R'--, --R'--CH.sub.2 --R'--, --R'--CO--R'--, --R'--SO.sub.2 --R'-- and --R'--S--R'--.
Said polyamides are capable of substantially complete imidization by heating, by which they form the polyamide-imide structure having, to a substantial extent, recurring units of: ##STR4## and units of: ##STR5## and, optionally, units of: ##STR6## wherein one carbonyl group is meta to and one carbonyl group is para to each amide group and wherein Z, R.sub.1, R.sub.2 and R.sub.3 are defined as above. Typical copolymers of this invention have up to about 50 percent imidization prior to annealing, typically about 10 to about 40 percent.
We can use a single diamine but, usefully, the mixture of diamines contains two or more, preferably two or three, wholly- or largely-aromatic primary diamines. More particularly, they are wholly- or largely-aromatic primary diamines containing from 6 to about 10 carbon atoms or wholly- or largely-aromatic primary diamines composed of two divalent aromatic moieties of from 6 to about 10 carbon atoms, each moiety containing one primary amine group, and the moieties linked directly or through, for example, a bridging --O--, --S--, --SO.sub.2 --, --CO--, or methylene group.
Preferably, the mixture of primary aromatic diamines comprises 2,2-bis[4-(p-aminophenoxy)phenyl]propane, bis[4-(p-aminophenoxy)phenyl]sulfone or a mixture of these in combination with diamines such as m-phenylene diamine, oxybis(aniline), neopentane diamine, trimethylhexamethylene diamine and the like. The preferred diamines for homo- and copolymers have the following formulae, 2,2-bis[4-(p-aminophenoxy)phenyl]propane, hereinafter referred to as BAPP, ##STR7## and bis[4-(p-aminophenoxy)phenyl]sulfone hereinafter referred to as BAPS. ##STR8## In the one-component system, the preferred diamines are oxybis(aniline), or meta-phenylenediamine. The aromatic nature of the diamines provides the excellent thermal properties of the copolymers while the primary amine groups permit the desired imide rings and amide linkages to be formed.
Usually, the polymerization or copolymerization is carried out in the presence of a nitrogen-containing organic polar solvent such as N-methylpyrrolidone (NMP), N,N-dimethylformamide, or N,N-dimethylacetamide. The reaction should be carried out under substantially anhydrous conditions and at a temperature below about 150.degree. C. Most advantageously, the reaction is carried out from about 30.degree. C. to about 50.degree. C.
The reaction time is not critical and depends primarily on the reaction temperature. It may vary from about 1 to about 24 hours, with about 2 to 4 hours at about 30.degree. C. to about 50.degree. C. preferred in the nitrogen-containing solvents.
Polyamide-imide polymers synthesized via the polycondensation of BAPS with trimellitic anhydride acid chloride (4-TMAC) have been shown to produce a unique polyamide-imide that does not require an annealing step to produce optimal physical properties. Long term thermal aging and annealing studies completed on the polyamide-imide have shown that the physical properties values remain relatively constant during annealing. This is in contrast to polyamide-imides prepared from 4-TMAC, oxybis(aniline) and m-phenylenediamine or from 4-TMAC, isophthalic acid and m-phenylenediamine in which an annealing heat treatment step is used to enhance the physical properties of the molded parts.
Furthermore, articles fabricated from polyamide-imide polymers based on BAPS may be remolded even after exposure to elevated temperature. This is in contrast to polyamide-imides described above that contain m-phenylenediamines which cannot be remolded or reworked due to imidization and/or crosslinking occurring during the post molding annealing treatment.
The polyamide-imide polymers based on BAPS do indicate that molecular weight appreciation takes place during molding and solid stating as evidenced by increased intrinsic viscosity of the polymer. Monofunctional end-capping reagents such as phthalic anhydride, aniline, trimellitic anhydride, and benzoyl chloride have been demonstrated to be useful in restricting the intrinsic viscosity appreciation of the polyamide-imide polymer during molding and annealing. Unexpectedly, about 1% to about 10% aniline and preferably about 1% to about 5% aniline was found to give significant improvements in polymer physical properties and in polymer melt processing by limiting the appreciation of the polymer melt viscosity.
The polyamide-imide resin composition of the present invention may optionally contain fillers. Fillers are added in order to improve heat resistance, mechanical properties, resistance to chemical substances, abrasion characteristics, electrical characteristics, flame retardation, etc. Suitable fillers include synthetic and natural compounds which are stable at temperatures of at least 300.degree. C., such as graphite, carborundum, silicon powder, molybdenum disulfide, fluorocarbon resin, glass fibers, carbon fibers, boron fibers, silicon carbide fibers, carbon whiskers, asbestos fibers, asbestos, metal fibers, antimony trioxide, magnesium carbonate, calcium carbonate, barium sulfate, silica, calcium metalsilicate, powders of metals such as iron, zinc, aluminum and copper, glass beads, glass balloons, alumina, talc, diatomaceous earth, clay, kaolin, gypsum, calcium sulfite, hydrated alumina, mica, other various kinds of metal oxides, inorganic pigments, etc.
For mixing and preparing compositions of the present invention containing fillers, it is possible to utilize an apparatus used for melt blending ordinary rubber or plastics, for example, Banbury mixers, brabenders and extruders. The mixing operations are continued until a uniform blend is obtained. The melt blending temperature is established at a value which is more than the temperature at which the blend system can be melted, but is less than the temperature at which thermal decomposition of the blend system begins. Melt blending temperatures are normally selected from the range of 250.degree.-400.degree. C., and preferably from the range of 300.degree.-380.degree. C.
Upon mixing and preparing filled compositions of the present invention, it is possible to separately supply the aromatic polyamide-imide resin, an optional thermoplastic resin component and optional fillers to the melt mixer. It is also possible to premix these materials using a mortar, Henschel mixer, ball mill or ribbon blender, and then supply the premix materials to the melt mixer.
Polyamide-imides prepared from 4-TMAC and BAPS, BAPP or mixtures of BAPS and BAPP with or without other diamines such as oxybisaniline, m-phenylenediamine, p,p'-methylene bis(aniline), neopentane diamine, trimethylhexamethylene diamine with an end capping reagent such as phthalic anhydride, trimellitic anhydride, aninile or benzoyl chloride, produce a polyamide-imide which does not require a solid stating or annealing step after molding to produce enhanced mechanical properties. However, these polyamide-imide polymers do exhibit extremely high melt viscosities making these polymers difficult to melt fabricate.
The processability of these end-capped BAPS containing amide-imide polymers can be significantly improved when these polymers are alloyed with one or more secondary polymer components with the secondary polymer components containing imide, ester, sulfone, amide or ether moieties.
Representative secondary polymer components by tradename included: Ardel D100, a polyarylate produced by Union Carbide Corp.; Radel A400, a polyarylsulfone produced by Union Carbide Corp.; Udel P1700, a polysulfone produced by Union Carbide Corp.; Victrex 5200, a polyethersulfone produced by ICI Inc.; and Ultem 1000, a polyetherimide produced by General Electric, Inc.
We have found that alloying about 1 to about 40 percent of a secondary polymer component listed above improves the melt flow properties of polyamide-imides prepared from BAPS, 4-TMAC with about 3 mole percent aniline as a capping agent, the latter polymer more conveniently referred to as BAPS/TMA-3% Aniline polyamide-imide hereinafter.
Additionally, it has been found that a particularly good balance of molded part physical properties and improvement of polymer melt flow properties is obtained when about 1 to about 5 percent by weight of an amorphous polyamide with the following recurring structure; ##STR9## was alloyed with the BAPS/TMA-3% Aniline polyamide-imide. The amorphous polyamide described above is manufactured by American Grilon Inc. under tradename of Grilamid TR 55 and was also marketed by Union Carbide Corporation under tradename of amidel. Trogamid-T, produced by Dynamit Nobel, has also been used.
The composition of the present invention forms a uniform melt blend and may be shaped by injection molding, extrusion molding, compression molding, or sintering molding.
For producing shaped articles utilizing injection molding or extrusion molding, machines equipped with a screw cylinder to promote excellent melt blending performance, it is not always necessary to separately prepare the blending composition in advance. By directly supplying the component materials to the screw hopper, either separately or after dry blending thereof, a shaped article of a uniform composition may be produced in one stage. However, the desired uniform blend can be more easily obtained by a two-stage blending method in which master-batch pellets are prepared by melt blending the filler with or without a secondary polymer component and desired thermoplastic resin component in advance, and then the master-batch pellets are further melt blended with the polyamide-imide resin component.
Shaped articles obtained by melt molding the heat resistant molding resin composition of the present invention exhibit excellent properties in terms of heat resistance, mechanical characteristics, electrical characteristics, sliding characteristics and solvent resistance characteristics, and may be utilized in many ways. They are useful as, for example, auto parts, electrical and electronic parts, water supplying and distributing machine parts, office machine parts, aircraft parts, and special machine parts.
Injection molding of the polyamide-imide polymer of the instant invention is accomplished by injecting the copolymer into a mold maintained at a temperature of about 300.degree. to 450.degree. F. In this process a 25 to 28 second cycle is used with a barrel temperature of about 600.degree. to 700.degree. F. The injection molding conditions are given in Table I.
TABLE 1 ______________________________________ Mold Temperature 350.degree. F. to 450.degree. F. Injection Pressure 15,000 to 19,000 psi and held for 1 to 3 seconds Back Pressure 100 to 220 psi Cycle Time 25 to 28 seconds Extruder: 600.degree. F. to 700.degree. F. Nozzle Temperature Barrels: 600.degree. F. to 700.degree. F. Front heated to Screw: 20 to 25 revolutions/min. ______________________________________
Cavity pressure measurements are used as quality control checks of polyamide-imide resin viscosity. Pressure buildup during the filling of an injection molded part is measured at a point in the cavity (ejector pin). This is accomplished by placing a pressure transducer behind the ejector pin and recording the pressure with a chart recorder or other readout device. Cavity pressure normally rises as the mold is being filled and peaks as the molten resin is packed into the cavity. As the resin solidifies, cavity pressure decreases.
We have found that resins that have low cavity pressures process poorly and that spiral flow measurements were not sensitive enough to discriminate between resins in the viscosity range of interest. Low cavity pressures indicate a large pressure drop between injection and cavity pressures. This indicates higher resin viscosities. In the same manner, high cavity pressures indicate less pressure change between injection and cavity pressures, suggesting lower resin viscosities.
Amide-imide polymer and copolymer viscosities had been measured by spiral flow determinations previous to the implementation of the cavity pressure procedure, see U.S. Pat. No. 4,224,214. Cavity pressure was selected over spiral because of its greater sensitivity. The cavity pressure test has been implemented as an amide-imide homopolymer and copolymer quality control procedure. Like spiral flow, cavity pressure is a test that can be done conveniently in a molder's shop.
A 40 MM Battenfield injection molding press can be used to evaluate the flow characteristics of a polymer at various fill rates and temperatures by measuring the flow time and pressure drop in the cavity. Table 1 above illustrates the processing conditions used to measure the polymer melt flow properties. The barrel temperature is maintained at a given temperature, 650.degree. or 700.degree. F., to obtain the melt viscosity measured in poises at the given temperature. A Daytronic 9010 open-loop mainframe monitor was used to measure the cavity pressure and fill time between the sprue and the dead-end of the flexural bars. Pressure transducers were fitted behind the knockout pins in the sprue and at the dead end of the flexural bar. The actual measurements were taken at the onset of the pressure rise at the dead end of the flexural cavity. The time to fill the cavity and the change in the pressure between the knockout pins is recorded and a melt viscosity is estimated at a given barrel temperature by multiplying the time and change in pressure with a device geometry constant. The constant is dependent on the mold geometry.
Resins were dried in a vacuum (2 mm Hg) oven at 300.degree. F. for at least 16 hours before testing. Moisture in amide-imide polymers has a very significant effect on its flow properties, therefore special care was taken to be sure the samples were properly dried. This drying procedure was used before making flow rate and cavity pressure measurements.
The flow rate procedure was patterned after the standard method described in ASTM D1238. A 335.degree. C. (635.degree. F.) barrel temperature with a 30 minute preheat time was used. This is about the largest set of weights that can be used safely with the standard extrusion plastometer apparatus with a standard 0.0825 in. diameter, and a 0.315 in. long orifice.
Special care was taken to be sure that each flow rate measurement was started when an equivalent volume of resin was in the barrel. Previous rheology work indicated that there is a very large "barrel height" effect on amide-imide homopolymers and copolymers. Each flow rate measurement was initiated while the top of the piston collar was between the two scribe marks on the piston. This precaution is also required by ASTM in method D1238.
The physical properties and test methods were as follows: Tensile Properties (ASTM D1708); Izod Impact (ASTM D256); Heat Deflection Temperature (ASTM 48); Inherent Viscosity (0.5 percent in NMP at 25.degree. C.); Absorbed water (equilibrium value at 160.degree. F.).